Raman and infrared spectroscopy of Sr2B′UO6 (B′ = Ni; Co) double perovskites

Abstract

Temperature dependent normal modes and lattice thermal expansion of the Sr 2 B'UO 6 (B' = Ni, Co) double perovskites were investigated by Raman/infrared spectroscopies and synchrotron Xray diffraction, respectively. Monoclinic crystal structures with space group P2 1 /n were confirmed for both compounds, with no clear structural phase transition between 10 and 400 K. As predicted for this structure, the first-order Raman and infrared spectra show a plethora of active modes. In addition, the Raman spectra reveal an enhancement of the integrated area of an oxygen stretching mode, which is also observed in higher-order Raman modes, and an anomalous softening of ~1 cm-1 upon cooling below T* ~ 300 K. In contrast, the infrared spectra show conventional temperature dependence. The band profile phonon anomalies are possibly related to an unspecified electronic property of Sr 2 B'UO 6 (B' = Ni, Co).

The Flexible Ba7UM2S12.5O0.5(M = V, Fe) Compounds: Syntheses, Structures and Spectroscopic, Resistivity, and Electronic Properties

“…First, the bands located between 300 and 400 cm –1 are assigned to the symmetric stretching vibrations in the FeS 4 or VS 4 tetrahedra. , Moreover, the signal is broadened significantly for Ba 7 UFe 2 ­S 12.5 O 0.5 , which we ascribe to its less symmetric structure compared with that of Ba 7 UV 2 ­S 12.5 O 0.5 . Such broadening is also evident in the region between 700 and 800 cm –1 , which we assign to the US 5 O octahedra by comparison to the data for the UO 6 unit in the perovskite structure type . The signal for Ba 7 UFe 2 ­S 12.5 O 0.5 at 700 cm –1 probably corresponds to the overlap of multiple vibration bands associated with the two different U sites in the structure.…”

“…Such broadening is also evident in the region between 700 and 800 cm −1 , which we assign to the US 5 O octahedra by comparison to the data for the UO 6 unit in the perovskite structure type. 68 The signal for Ba 7 UFe 2 S 12.5 O 0.5 at 700 cm −1 probably corresponds to the overlap of multiple vibration bands associated with the two different U sites in the structure. The Raman spectrum of Ba 7 UFe 2 S 12.5 O 0.5 also shows the characteristic vibration of the S−S bond, located at about 450 cm −1 .…”